1. Field of the Invention
The present invention relates to a starter for an engine and, more particularly, to a coaxial type starter used to start the engine of a vehicle.
2. Description of the Prior Art
Conventional starters used to start the engine of a vehicle have heretofore been arranged as shown in FIG. 3.
The conventional starter 1 shown in FIG. 3 comprises a d.c. motor 2, an overrunning clutch 4 slidably fitted on an extended shaft portion 3a of an armature rotary shaft 3, and a shift lever 8 having one end thereof engaged with a plunger rod 6 of an electromagnetic switch 5 disposed at one side of the d.c. motor 2 and the other end thereof engaged with an annular member 7 secured to the overrunning clutch 4. The shift lever 8 causes the overrunning clutch 4 to slide on the extended shaft portion 3a of the armature rotary shaft 3.
However, the conventional starter 1 needs the shift lever 8 and the electromagnetic switch 5 which actuates the shift lever 8 and also turns on the power supply for the d.c. motor 2 is disposed at the side of the d.c. motor 2, that is, the starter 1 has the so-called biaxial arrangement. Therefore, the kinds of engine layout that can be adopted in designing a vehicle have heretofore been restricted to a substantial extent.
In order to avoid the above-described problem, it has been proposed that the electromagnetic switch be disposed at one axial end of the d.c. motor to thereby give the starter a simple configuration such as a relatively long and narrow cylindrical shape. According to this proposition, the starter is basically arranged such that the plunger rod of the electromagnetic switch which has heretofore been used to actuate the shift lever extends into the passage extending as far as the output rotary shaft inside the armature rotary shaft. Since the armature rotary shaft of the d.c. motor and the rod of the electromagnetic switch are disposed on the same axis, this starter is known as the coaxial type starter.
In order to shorten the axial length and thereby reduce the size of the coaxial type starter having the above-described basic arrangement, a starter for an engine has been proposed wherein an overrunning clutch is incorporated inside an armature rotary shaft which constitutes an armature of a d.c. motor.
In the engine starter having the overrunning clutch incorporated in the armature rotary shaft, an annular recess is formed on the inner wall of the armature rotary shaft, and a plurality of cam surfaces are formed on the cylindrical wall of the recess. Thus, there are wedge-shaped spaces which are defined between the cam surfaces and a clutch inner member received inside the armature rotary shaft, and a roller and a spring for pressing the roller are disposed in each of the wedge-shaped spaces. In other words, this starter is arranged such that the armature rotary shaft also serves as a clutch outer member of the overrunning clutch.
The above-described conventional engine starter suffers, however, from the following problems. Namely, if the overrunning clutch is disposed inside the armature rotary shaft in order to reduce the overall size or length of the starter, the outer diameter of the armature rotary shaft is significantly increased, resulting disadvantageously in an increase in the overall diameter of the engine starter.